Create subtype reduction rules for assertion functions

Bug Report

🔎 Search Terms

inference assert

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about Common "Bugs" That Aren't Bugs

⏯ Playground Link

Playground link with relevant code

💻 Code

function Test<X extends any>(params: X[]) {}
function Test2<InParams extends readonly any[]>(params: InParams) {}

function f1(a: any): number {return 1}
function f2(a: any): string {return "string"}
function f3(a: any) {return {k: 1}}

function a1(a: any): asserts a is number {}
function a2(a: any): asserts a is string {}
function a3(a: any): asserts a is {k: number} {}

const aifwe = [f1, f2, f3]
Test([f1, f2, f3])
Test([a1, a2, a3])
Test2([f1, f2, f3])
Test2([a1, a2, a3])

🙁 Actual behavior

The Test and Test2 calls are inferred as (in order):

• function Test<((a: any) => number) | ((a: any) => string) | ((a: any) => { k: number; })>(params: (((a: any) => number) | ((a: any) => string) | ((a: any) => { k: number; }))[]): void
• function Test<(a: any) => asserts a is number>(params: ((a: any) => asserts a is number)[]): void
• function Test2<(((a: any) => number) | ((a: any) => string) | ((a: any) => { k: number; }))[]>(params: (((a: any) => number) | ((a: any) => string) | ((a: any) => { k: number; }))[]): void
• function Test2<((a: any) => asserts a is number)[]>(params: ((a: any) => asserts a is number)[]): void

🙂 Expected behavior

For the assert calls to also be inferred as unions.

This is also irregular since with the wrong inference, I would expect the other functions to be marked as errors, since they have different type signatures.

Comienza con el ejemplo vinculado de TypeScript Playground y sigue la inferencia genérica para arrays de funciones de aserción, centrándote en las reglas de reducción de subtipos solicitadas. Se considera terminado cuando las llamadas de aserción de Test y Test2 infieren uniones como las llamadas de funciones ordinarias, con el comportamiento de inferencia relevante cubierto por una prueba de regresión.